S-antigen is a well-characterized retinal protein, intimately involved in the visual process, and highly pathogenic for the induction of experimental autoimmune uveitis (EAU), and intimately involved in the phototransduction of vision. In order to more fully understand structure/function relationships of S- antigen in the pathogenesis of EAU and in the phototransduction of vision we have (1) produced monoclonal antibodies (MAbs) which define different epitopes of S-antigen, (2) determined the amino acid sequence of bovine S-antigen, (3) localized one MAb binding site and (4) localized two uveitopathogenic sites in bovine S-antigen. In our laboratory, we have generated two MAbs, MAbA9-C6 and MAbA1-G5, which define different epitopes of S-antigens. These MAbs have been useful in our studies concerning S-antigen in the developing retina, pineal gland and in tumors arising from these tissues. The amino acid sequence of bovine S-antigen has now been determined. Analysis of our sequence data has revealed that; S-antigen exists primarily in a beta sheet conformation; contains two potential phorphorylation sites; three potential carbohydrate attachments sites; an ADP-ribosylation site; and sequence homologies to tranducin, another protein in the visual pathway. Such information is essential in order to understand the role of S-antigen in the phototransduction of vision. A knowledge of the amino acid sequence has also led to the identification of the MAbA9-C6 binding site and two uveitopathogenic sites. Peptides, corresponding to the amino acid sequence of S-antigen, have been synthesized chemically and two peptides designated peptide K and peptide M have been found to be highly uveitopathogenic. Immunization of Lewis rats with microgram amounts of either peptides induced an EAU which was clinically and histopathologically indistinguishable from the EAU induced by native S-antigen. In this continuation proposal we plan to refine and expand our initial observations regarding the uveitopathogenic sites in bovine, human and rat S-antigen. In addition, we propose to produce MAbs against the uveitopathogenic determinants and to refine the MAbA9-C6 binding site to the resolution of a single amino acid. These studies and the reagents we are developing will not only aid in understanding the role of S-antigen in the pathogenesis of EAU, but in the phototransduction of vision as well.